Based on the classic Irv Weiner Guillo-Card, here's an inexpensive version of this excellent effect.
Show a packet of four cards, and call attention to the hole cut through the middle of each card -- a hole just big enough for a finger to stick through it. The packet of cards is squared, so the holes are aligned. One card is drawn upward and the spectator puts her finger through the holes in the main packet. Then the extended card is pushed down and through her finger. The cards are pulled off the front of her finger one at a time and she can see the "blade" card is now surrounding her finger!
Complaint: well, this trick is made with inexpensive bridge-size playing cards, and although they work fine, I wish it had been made with a familiar brand like Bicycle. But maybe laymen don't really notice stuff like this... Once you know the working, it is fairly easy to make this up in any brand of cards. (The hard part is cutting the circles out, but they have the right tool for this at any good craft store.) But, again, the cards supplied work fine, and create the desired magical effect.
Brand new and unused, with instructions.